1. Field of the Invention
The present invention relates to an image pickup device and an evaluation value generating device.
Priority is claimed on Japanese Patent Application No. 2011-200665, filed Sep. 14, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
In recent years, as image pickup devices such as digital cameras have become faster, cases in which solid-state devices (hereinafter referred to as “imagers”) that simultaneously output signals (hereinafter referred to as “pixel signals”) of a plurality of pixels are mounted on image capturing units of such image pickup devices have increased. Examples of output methods of the imager in which a plurality of pixel signals are simultaneously output include an output method of simultaneously outputting pixel signals of two horizontally adjacent pixels and an output method of simultaneously outputting pixel signals of two vertically adjacent pixels.
With the advance in performance of next-generation image pickup devices, various methods of outputting the pixel signals from imagers are considered. However, even when there is a difference between the output methods of outputting the pixel signals from the imagers, image capturing processing units (so-called image capturing sub-systems) located on the rear stage to process the pixel signals preferably have the same configuration to correspond to the imagers that realize various output methods.
Accordingly, for example, Japanese Unexamined Patent Application, First Publication No. 2008-005048 discloses a technology for a method of outputting pixel signals corresponding to different imagers. FIG. 8 is a block diagram illustrating the overall configuration of an image pickup device in accordance with the related art, as disclosed in Japanese Unexamined Patent Application, First Publication No. 2008-005048. The image pickup device in accordance with the related art includes image capturing processing units (first and second image processing units) corresponding to the number of channels (in FIG. 8, two channels) of image data output from an image capturing unit so as to be configured to correspond to an imager that simultaneously outputs a plurality of pixel signals.
In the image pickup device in accordance with the related art, a decimation unit is added to each of evaluation value calculating units (an AE evaluation value calculating unit and an AF evaluation value calculating unit) configured to correspond to an image capturing unit in which the number of channels of image data to be output is one (1 ch) to realize the output method of the imager in which the plurality of pixel signals are simultaneously output. The evaluation value calculating units generate evaluation values after the decimation units of the evaluation value calculating units perform a process of selecting (decimating) a plurality of simultaneously input image data (in FIG. 8, two pieces of image data).
FIG. 9 is a block diagram illustrating the overall internal configuration of the evaluation value calculating units of the image pickup device in accordance with the related art. Of the evaluation value calculating units of the image pickup device, the configuration of the AF evaluation value calculating unit is shown in FIG. 9. When an AF evaluation value is generated, a first decimation unit first performs the decimation process on the image data output from the image capturing unit. More specifically, when the image pickup device includes a type of imager that simultaneously outputs pixel signals of two horizontally adjacent pixels, the first decimation unit performs the decimation process on image data in the horizontal direction. On the other hand, when the image pickup device includes a type of imager that simultaneously outputs pixel signals of two vertically adjacent pixels, the first decimation unit performs the decimation process on image data in the vertical direction.
Thereafter, the AF evaluation value calculating unit calculates (generates) an AF evaluation value of the image data obtained through the decimation process. More specifically, a Y generating unit of the AF evaluation value calculating unit first generates luminance signals (Y signals) based on the image data obtained through the decimation process. Then, a vertical AF evaluation value generating unit of the AF evaluation value calculating unit performs a vertical filtering process on the luminance signals generated by the Y generating unit and generates a vertical AF evaluation value by accumulating the luminance signals obtained through the filtering process. Simultaneously, a horizontal AF evaluation value generating unit of the AF evaluation value calculating unit performs a horizontal filtering process on the luminance signals generated by the Y generating unit and generates a horizontal AF evaluation value by accumulating the luminance signals obtained through the filtering process.
Accordingly, the image pickup device in accordance with the related art having the above-described configuration can calculate (generate) the AF evaluation value or the AE evaluation value with no increase in the circuit size of the evaluation value calculating units, even when image data corresponding to the pixel signals of a plurality of pixels is simultaneously input to the evaluation value calculating units.
However, since the evaluation value calculating units of the image pickup device in accordance with the related art disclosed in Japanese Unexamined Patent Application, First Publication No. 2008-005048 calculate the evaluation values after the decimation process, there is a problem that the accuracy of the generated evaluation values may deteriorate depending on a method for the decimation process.
In particular, since the AF evaluation value calculating unit shown in FIG. 9 calculates the evaluation value based on vertical or horizontal frequency components included in the image data, the accuracy of the evaluation value may be different between the simultaneously generated vertical AF evaluation value and horizontal AF evaluation value. More specifically, when the image pickup device includes a type of imager that simultaneously outputs pixel signals of two horizontally adjacent pixels, the first decimation unit performs the decimation process on image data in the horizontal direction. Therefore, the accuracy of the vertical AF evaluation value calculated based on the vertical frequency components does not deteriorate, but the accuracy of the horizontal AF evaluation value calculated based on the horizontal frequency components may deteriorate.
On the other hand, when the image pickup device includes a type of imager that simultaneously outputs pixel signals of two vertically adjacent pixels, the first decimation unit performs the decimation process on image data in the vertical direction. Therefore, the accuracy of the horizontal AF evaluation value calculated based on the horizontal frequency components does not deteriorate, but the accuracy of the vertical AF evaluation value calculated based on the vertical frequency components may deteriorate.
In the method of performing the decimation process on the image data in a fixed manner in accordance with the related art, the accuracy of the evaluation value may sometimes deteriorate depending on the output methods of outputting the pixel signals output by the imager of the image pickup device. Since the deterioration in the accuracy of the evaluation values also results in deteriorating the performance of the image pickup device, it is preferable for the accuracy of the evaluation values not to deteriorate.
A method of calculating the evaluation values without performing the decimation process can be considered as a method of preventing the accuracy of the evaluation values from deteriorating. In this method, the accuracy of the evaluation values can be improved compared to the method in accordance with the related art, but times necessary to calculate the evaluation values may be lengthened. Accordingly, a method of equalizing the times necessary to calculate the evaluation values by increasing the operation speed of the evaluation value calculating units can be considered. In this method, however, the power consumption of the evaluation value calculating units may increase, since the operation speed of the evaluation value calculating units is required to increase. Thus, the method of calculating the evaluation values without performing the decimation process by increasing the operation speed of the evaluation value calculating units is not necessarily an optimum method of preventing the accuracy of the evaluation values from deteriorating.